1. Field of the Invention
The present invention relates to a device photosensitive to infra-red radiation.
This device may comprise a two-dimensional mosaic of detectors, distributed in M lines and N columns, or it may comprise a bar or single line of N detectors.
2. Prior Art
A variety of devices which are photosensitive to the infra-red range are known in the prior art.
The operation of three of these devices will be recalled briefly in the following.
A device in which each detector is associated with an MOS transistor became known from the article entitled "Electronically scanned CMT detector array for the 8-14 .mu.m band" which appeared in the periodical "Electronics Letters" of Apr. 1, 1982, volume 18, number 7, pages 285 to 287. A shift register enables each line of detectors to be addressed successively via MOS transistors. The charges derived from the detectors of the line addressed are stored by means of a series of operational amplifiers arranged as integrators, each amplifier being connected via MOS transistors to the detectors of one and the same column. A multiplexer enables sequential reading of the integrators, whereupon another line of detectors is addressed by the register.
It should be observed that, in a device of this kind, the integration of the charges is performed successively for each line of detectors by the same amplifiers arranged as integrators. The period of integration of the charges originating from each detector is therefore greatly limited. Another disadvantage of a device of this kind is that the operational amplifiers cannot be positioned in the cryostat enclosing the detectors and the remainder of the device. This cryostat consequently comprises numerous low-level outputs.
A device of another type is known from the article entitled "CCD readout of infrared hybrid focalplane arrays", published in the periodical "I.E.E.E. Transactions on Electron Devices", volume ED27, number 1, January 1980, pages 175 to 188. In this device--see FIG. 2 of the article quoted--each detector is associated with a capacity for storage of the charges which is connected to one of the inputs of a charge transfer register.
In a device of this type, all the lines of detectors are addressed simultaneously so that the contents of the storage capacities may be transferred into the shift registers having their inputs in parallel and their outputs in series. The outputs of these registers are connected to the inputs of another charge transfer shift register of the series output type, which delivers the output signal of the device. In a device of this nature, the period of integration of the charges may be substantial and the device as a whole may be contained within a cryostat. The disadvantage of a device of this kind is, in particular, that a loss of information occurs because of the inefficiency of transfer of the charge transfer registers. This inefficiency is increased by the very low temperature, 77K for example of the cryostat and by the great number of transfers to be performed, for example 400 transfers for 100 detectors. Another disadvantage of a device of this type is its bulk.
For each detector, the charges must be stored in a storage capacity during the integration period, and then in a shift register during the readout period. Two storage surfaces are thus needed for each detector.
Finally, this review of different kinds of devices which are photosensitive to infra-red radiation, will be completed by the devices in which the integration of the charges is performed in the detectors operating in the so-called "VIDICON" mode. An operation of this nature yields poor performances in the case of infra-red detectors, in particular of those which are sensitive in the 8-12 .mu.m band.